The present disclosure relates to subject matter contained in Japanese Patent Application P2001-328966 filed on Oct. 26, 2001, which is expressly incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a thermal link assembly and a cryostat using a plurality of the thermal link assemblies.
2. Description of the Related Art
There have been used radio telescopes operating in the millimeter to submillimeter wavelength range, which have a receiver system including receivers corresponding to a plurality of observational bands. In order to acquire more detailed information about a more distant target astral body, some radio telescopes are designed to include such a receiver system that uses superconducting-tunnel-junction (SIS) mixer front-ends, which advantageously provide extremely low noise operation. In order to ensure superconductivity, SIS mixer front-ends have to be housed in a cryostat for maintaining them at a cryogenic temperature, such as 4 K for example.
A cryostat for such a receiver system is described by A. Orlowska, M. Harman, and B. Ellison, xe2x80x9cReceiver Cryogenic System,xe2x80x9d ALMA Project Book, chapter 6, Jan. 29, 2001, which is available as a pdf file at http://www.alma.nrao.edu/projectbk/construction/.
The cryostat described by Orlowska et. al. includes a vacuum container that provides thermal insulation, radiation shielding and cryogenic heat lift. Three temperature stages are constructed within the vacuum container. Each temperature stage has a metallic base plate having a good heat conductivity. The base plates of the temperature stages are arranged parallel to each other in a stacked fashion and are cooled by a cryogenic cooler having three cold stages.
In the cryostat of Orlowska et. al., the radio frequency and other electronic components that form an individual receiver corresponding to a specific observational band are integrated into an autonomous support structure called a xe2x80x9ccartridge,xe2x80x9d which is adapted for insertion into and removal from the vacuum container through an insertion hole formed in the bottom end plate of the container. The base plates of the temperature stages have holes for receiving the cartridges. Each cartridge has three disk-shaped metallic xe2x80x9ccold platesxe2x80x9d arranged in a stacked fashion. On the top cold plate of a cartridge, various electronic components are mounted. Further, the three cold plates of a cartridge form part of the corresponding three temperature stages, so that the three cold plates have to be thermally connected with the corresponding base plates. This is achieved through thermal link assemblies. The thermal link assembly is a ring-shaped assembly having an inner cylindrical surface to be in contact with the peripheral cylindrical surface of the disk-shaped cold plate. The thermal link assembly is attached to one base plate and receives one cold plate, so as to provide thermal connection between them.
The thermal link assembly described by Orlowska et. al., however, suffers from several drawbacks including providing only insufficient thermal conduction properties, being relatively heavy in weight and relatively massive in size and requiring relatively high manufacturing costs.
In view of the foregoing, it is an object of the present invention to provide a thermal link assembly which may provide good thermal conduction properties, may be relatively light in weight and relatively compact in size, as well as may be manufactured at relatively low costs.
It is another object of the present invention to provide a cryostat using such thermal link assemblies.
In accordance with the present invention, there is provided a thermal link assembly for providing thermal connection between first and second thermally conductive parts. The thermal link assembly is adapted to be secured to the first part. The second part is generally disk-shaped and has a peripheral cylindrical surface. The thermal link assembly comprises an annular ring made of thermally conductive material. The annular ring is generally in a shape of a revolution with respect to an axis. The annular ring includes an annular base portion to be secured to the first part and a series of contact tongues arranged along the base portion. Each contact tongue has a stem and a head. The stem has i) a longitudinal axis extending generally parallel to the axis of the annular ring, ii) a first longitudinal end connected to the base portion, and iii) a second longitudinal end connected to the head. The head has a contact surface which contacts the peripheral cylindrical surface of the second part. The stem is capable of twisting and bending elastic deformation with respect to the longitudinal axis, so that the contact surface of the head is capable of tilting in any direction and displacing in the radial direction of the annular ring. Finally, the thermal link assembly further comprises an annular band fitted around the annular ring for exerting a force to the head of each contact tongue so as to urge the contact surface of the head against the peripheral cylindrical surface of the second part.
The annular ring may further include i) an annular proximal portion defining an inner cylindrical surface and ii) a thin-wall cylindrical intermediate portion connecting the base portion and the proximal portion. In such case, the annular ring may have a plurality of axial slits formed at fixed circumferential intervals. Each axial slit extends from adjacent the base portion, across the thin-wall cylindrical intermediate portion and throughout the annular proximal portion, so that i) a region of the thin-wall intermediate portion between adjacent two of the axial slits defines the stem of each contact tongue, ii) a region of the annular proximal portion between adjacent two of the axial slits defines the head of each contact tongue, and iii) a region of the inner cylindrical surface between adjacent two of the axial slits defines the contact surface of the head of each contact tongue.
The annular ring may be made of metallic material. The inner cylindrical surface of the annular ring may have a diameter in a range 100 to 300 mm. The stem of each contact tongue may have a constant thickness as measured in the radial direction of the annular ring and a constant width as measured in the circumferential direction of the annular ring. In such case, the stem of each contact tongue may have a thickness in a range 0.2 to 0.8 mm, a width in a range 2.5 to 15 mm and a length in a range 5 to 50 mm.
In case where the inner cylindrical surface of the annular ring has a diameter in a range 100 to 200 mm, the stem of each contact tongue may have a thickness in a range 0.2 to 0.5 mm, a width in a range 2.5 to 8 mm and a length in a range 5 to 30 mm.
In accordance with the present invention, there is also provided a cryostat for a receiver system used in a radio telescope. The cryostat comprises: a vacuum container; a plurality of cartridges capable of insertion into and removal from the vacuum container, each cartridge having i) at least one thermally conductive cold plate which is generally disk-shaped and has a peripheral cylindrical surface and ii) a receiver mounted on the cold plate; at least one temperature stage constructed in the vacuum container, the temperature stage having a thermally conductive base plate; a cryogenic cooler for heat lift of the temperature stage; and a plurality of thermal link assemblies, each secured to one of the base plates and providing thermal connection between the base plate and one of the cold plates. Each thermal link assembly comprises an annular ring made of thermally conductive material. The annular ring is generally in a shape of a revolution with respect to an axis. The annular ring includes an annular base portion to be secured to the base plate and a series of contact tongues arranged along the base portion. Each contact tongue has a stem and a head. The stem has i) a longitudinal axis extending generally parallel to the axis of the annular ring, ii) a first longitudinal end connected to the base portion, and iii) a second longitudinal end connected to the head. The head has a contact surface adapted to be in contact with the peripheral cylindrical surface of the cold plate. The stem is capable of twisting and bending elastic deformation with respect to the longitudinal axis, so that the contact surface of the head is capable of tilting in any direction and displacing in the radial direction of the annular ring. Finally, the thermal link assembly further comprises an annular band fitted around the annular ring for exerting a force to the head of each contact tongue so as to urge the contact surface of the head against the peripheral cylindrical surface of the cold plate.
For the above cryostat, the annular ring may further include i) an annular proximal portion defining an inner cylindrical surface and ii) a thin-wall cylindrical intermediate portion connecting the base portion and the proximal portion. In such case, the annular ring may have a plurality of axial slits formed at fixed circumferential intervals. Each axial slit extends from adjacent the base portion, across the thin-wall cylindrical intermediate portion and throughout the annular proximal portion, so that i) a region of the thin-wall intermediate portion between adjacent two of the axial slits defines the stem of each contact tongue, ii) a region of the annular proximal portion between adjacent two of the axial slits defines the head of each contact tongue, and iii) a region of the inner cylindrical surface between adjacent two of the axial slits defines the contact surface of the head of each contact tongue.